The present invention relates to exhaust gas recirculation in the automotive internal combustion engine and more particularly to a means for cooling the exhaust gas that is returned to the combustion cycle. Since approximately 1971, automotive vehicle manufacturers have been required to add an ever-increasing number of components or systems to the vehicle or the internal combustion engine therein to increase the safety of the vehicle or decrease the emissions inherent in the exhaust gases from the internal combustion engine. Such components include positive crankcase ventilation, exhaust gas recirculation, an evaporation control system and a catalytic converter in the exhaust line.
Of major concern are the emissions from the exhaust gas of an internal combustion cycle which have been blamed for conditions such as smog occurring in large cities where a large number of automobiles are present each day. The oxides of nitrogen are one such emission, and an exhaust gas recirculation cycle is used to reduce these oxides present in the engine exhaust. Formation of nitrogen oxides takes place at very high temperatures and consequently occurs during the peak temperature period of the combustion process. To reduce and control nitrogen oxides formation, only a slight reduction in peak temperature is required.
This temperature reduction can be accomplished by introducing small amounts of an inert gas into the combustion process and, as the end products of combustion provide a continuous supply of relatively inert gases, it becomes a matter of utilizing those gases in the correct proportion. Thus, a recirculation passage is connected to the exhaust manifold and to a vacuum modulated shut-off and metering valve installed on the inlet manifold to control the flow of exhaust gases. The recirculation or additional exhaust gas passages are closely positioned to the engine or may be cast into the complex runner system of the inlet manifold.
However, the exhaust gases from the internal combustion engine cycle are still at a very high temperature level and it is desirable to substantially reduce that temperature level before the gases are reintroduced into the combustion cycle. The present invention accomplishes this desired temperature reduction.